Soft contact lenses are produced by a number of methods including static cast molding, spincasting, lathing and combinations of casting and lathing. A critical step in the production of lense using molds is releasing the lens from the mold without damaging the lens. One method of lens release is to hydrate the lens. The lens-in-mold assembly is placed in a hydration tank filled with water. The water is usually heated.
Often hydration alone does not release the lenses from the molds. The lenses must then be gently removed from molds by hand. Such hand-assisted lens removal increases the liklihood of lens damage. These damaged lenses often fail the subsequent quality inspections due to tearing, nicks, or other surface defects which occur as the lenses are released from the molds. One surface defect which is prevalent and which is commonly measured is known as the POM (piece of material) defect. This defect occurs as a result of excess polymer debris adhering to the lens. In essence, the POM defect causes an irregular surface on the lens due to an additional piece of material adhering to the lens.
A method of improving the release rate and decreasing the incidence of POM defect by facilitating the release of spincast and castmolded lenses which, in turn, would significantly increase the useable lens yield for such lenses, is not known. This invention addresses the problem of undesirably low cosmetic yields of contact lenses during hydration release.